Coastal Shoreline Change

Monitoring Objectives

• Measure the position of ocean- and sound-side shorelines
• Identify coastal erosion hotspots in ocean- and sound-side shorelines within network parks

Background
The problem of land loss/gain and landscape alteration at the marine edge is fundamental to the many issues facing coastal park resource stewards. Shoreline change is a prime geo-indicator of coastal environmental resource threats within parks. Change in shoreline position drives the alteration and replacement of established natural habitats and shoreline retreat may destroy cultural resources, facilities, and other infrastructure where they exist. Geomorphologic change is a basic concern because it also drives change in other natural resource areas of interest within the NPS program: water quality in ground and in estuaries, species and habitats of concern, recreational visitor use, and even resource extraction. Spatial variability is inherent in shoreline change. Early identification of changes in past trends, along with an understanding of normal variability, is critical for the recognition of ecological problems in coastal parks. For managers, an understanding of the spatial and temporal patterns of geomorphologic change is basic to optimal management of any coastal park because: 1) the interface of marine and land systems is very dynamic and is driven by multiple forcing mechanisms, 2) it results in alterations to resource patterns and dynamics at habitat and ecosystem level, and 3) it will eventually result in the loss of static resources.

Monitoring Approach
Shoreline change will be measured in one of two ways: through GPS positional and attitude measurements of shorelines on the foreshore, and through change detection of remotely sensed data on the sound-side shore. Mapping will occur annually to semi-annually and following storm events.

GPS Measurements. To determine park-wide trends in shoreline movement, a sampling design that includes all ocean shorelines and selected sandy beach bay/estuary areas will be used following protocols developed by the United States Geological Survey (USGS) (List et al. Unpublished). SECN will monitor the horizontal position of mean high water (MHW) contour using the measurement system SWASH (Surveying Wide Area Shorelines). SWASH consists of GPS positioning and a GPS-based attitude sensor mounted on an amphibious all-terrain vehicle (ATV), which is driven along the beach foreshore at low tide. Vehicle attitude and position in three dimensions are used to calculate the horizontal location of the MHW contour through linear extrapolation from the position of the vehicle track. Contour positioning errors are estimated by two approaches: a standard method whereby bulk statistics are used to estimate a 95% confidence interval, and a local method for estimating error that depends on the local beach slope and the deviation between the ATV track height and the target MHW elevation. The standard method gives an estimate of shoreline positioning error on the order of +/-1.6 meters. The local method provides error increases as the vehicle track deviates significantly from MHW. The SWASH system can survey up to 70 km of coast within the 3-4 hours bracketing low tide, and is ideal for rapid-response measurements of storm impacts as well as for repetitive shoreline survey programs over longer periods. Data collected by SWASH is compatible with LIDAR (Light Detection and Ranging) based shoreline studies.

Remote Sensing. Change detection methods and GPS ground surveys will be used to estimate sound-side shoreline change over time using remotely sensed data from a variety of sources. The SECN is currently working with the University of Georgia Natural Resource Spatial Analysis Lab on change detection imagery acquisition on processing, based on existing methodologies and technologies. The frequency at which remotely-sensed data will be collected will vary from park to park, but will occur at a minimum of once every three years at parks where shorebird habitat will also be monitored through remote sensing methods.

Parks Where Protocol Will be Implemented
Cape Hatteras National Seashore (CAHA), Cape Lookout National Seashore (CALO), Fort Sumter National Monument (FOSU) , Fort Pulaski National Monument (FOPU), Fort Frederica National Monument (FOFR), Cumberland Island National Seashore (CUIS), Timucuan Ecological and Historic Preserve (TIMU), Fort Matanzas National Monument (FOMA) and Canaveral National Seashore (CANA)

Principal Investigator
Tony Curtis, Coastal Ecologist